CILIARY MECHANISMS OF LAMELLIBRANCHS 651 
wall possesses a general ciliation (fig. 14), material being carried 
down, posteriorly, to the thickening of the fused edges, and then 
sharply forward; while over the upper and anterior part of the 
wall, everything is carried directly to a vortex (v) near the foot 
opening. Figure 15 represents a ventrally directed view of the 
anterior portion of the fused edges. In addition to a general 
ciliation, several distinct lines (7) lead to a vortex (v), and here 
accumulate balls of mucus with entangled particles, which 
sometimes attain a diameter of four or five millimeters. When 
these whirling balls happen to topple over toward the fused edges, 
they are caught up by a line of cilia (y), and carried on to a broad 
tract (me), which conducts them swiftly backward to a bay below 
the base of the siphon, as in most bivalves. Ultimately they 
are discharged through the incurrent siphon as described for 
Schizotherus. 
Variation in mantle ciliation of different forms is greater than 
in other organs. Here the vortices seem to characterize Mya 
and its near relatives. 
Platyodon cancellatus Conrad 
This species occurs on the coast of California. Though found 
in burrows of soft sandstone, or similar rock—and apparently 
not elsewhere—it is not a true borer, but a nestler in the exca- 
vations of borers. It attains a length of about three inches, 
and is much like Mya in appearance. The ciliation of all of its 
organs is practically identical with that of Mya. The general 
courses of gill and palp currents are shown in figure 16. On the 
side of the visceral mass, somewhat below its center, is what 
appears to be a poorly developed vortex. Very little material 
stops here, however, most of it being carried down to the ventral 
wall, a short distance behind the very small, hatchet shaped foot, 
Fig. 15 Mya arenaria; mantle edge from above; 2, ciliated tracts to mantle 
vortex; v, single tract from vortex to ventral mantle. 
Fig. 16 Platyodon cancellatus; b, bay of mantle; f, foot; fo, foot opening; 
g, gill; p, anterior palp; s, siphon; v, mantle vortex. 
Fig. 17 Platyodon cancellatus; mantle edge from above; letters as in figure 15. 
